The operation of vehicles by persons under the influence of alcohol is a major safety problem in the United States and many other countries. Despite growing public awareness and government concern, statistics continue to show that a high percentage of automobile accidents causing serious injury or death involve drivers who have been drinking alcoholic beverages in excess. Injuries in the workplace are also often found to be related to the operation of heavy equipment or other machinery by persons impaired by the effects of alcohol.
To address this problem, various attempts have been made to develop devices intended to prevent automobiles and the like from being operated by inebriated individuals. Such devices, which are commonly referred to as "sobriety interlocks" are often based on the well known principle that the gas present in the alveoli of the lungs has an alcohol content directly proportional to that of the bloodstream. Blood alcohol content (BAC) thus can be accurately determined by breath testing. A sobriety interlock is connected to the vehicle and normally operates to prevent the vehicle from being started unless one or more prerequisite conditions imposed by the interlock are satisfied. Foremost among such conditions is that any alcohol detected be present in a sufficiently low concentration although, the interlock may normally require any number of further conditions to be met before starting of the vehicle is enabled.
For example, it is generally acknowledged that to accurately determine BAC from a breath sample, an interlock must be designed to require delivery of a "deep lung" breath sample. As used herein, that term refers to a breath sample consisting of a proportion of alveolar gas sufficient to permit an accurate determination of blood alcohol concentration. Since breath expired from upper portions of the respiratory tract does not necessarily have an alcohol level proportional to that of the bloodstream, a deep lung sample is essential if an interlock is not to be defeated by shallow exhalations of a series of short puffs of breath expelled from upper portions of the respiratory tract.
This problem is addressed effectively in U.S. Pat. Nos. 4,093,945 and 3,764,270 issued to Collier et al. The Collier et al. patents disclose means, such as a pressure switch and timer system, to ensure delivery of an essentially continuous and uninterrupted flow of breath sufficient to yield a deep lung sample. The sampling interval determined by the timer and the flow rate (as measured by the pressure sensor or other flow sensing means) are selected together to ensure a deep lung sample will be given. Unless breath is delivered at at least a minimum predetermined flow rate without interruption for the entire sampling interval, a required condition is not deemed satisfied and the vehicle cannot be started.
Unlike breath analyzer tests which are usually administered under the supervision of police or other trained persons, sobriety interlocks are routinely used outside the presence of persons other than the vehicle operator/test subject whose use of the interlock may be less than completely voluntary. One example of such a situation is where an employer seeks liability protection by installing interlocks on vehicles operated by employees. A higher degree of compulsion may be involved in some cases of court-supervised rehabilitation of offenders found to have been driving while under the influence of alcohol (DUI). As a mandatory condition for permitting a DUI offender to drive in order to maintain employment and/or obtain counselling, some courts may require a sobriety interlock to be installed in the offender's car. In such cases there is an increased likelihood that attempts to defeat the interlock will be made. Accordingly, the prior art has proposed various self-supervisory techniques directed toward avoiding circumvention of interlocks by various forms of subterfuge. These techniques typically share a common characteristic in that they require one or more additional conditions, usually unrelated to alcohol to be satisfied as prerequisites to starting the vehicle.
For example, techniques to discriminate between a contemporaneous breath sample and bogus gasses such air from a bicycle pump, filling station air hose or breath from a previously inflated balloon are discussed in U.S. Pat. Nos. 4,592,443; 3,831,707; and 3,824,537. Each of these patents proposes requiring one or more additional conditions be satisfied before permitting the vehicle to start. U.S. Pat. No. 4,592,443 requires the temperature of the gas delivered for a test to fall within a range expected for breath. Breath being moist, U.S. Pat. No. 3,831,707 requires the gas to contain appropriate humidity to avoid circumventing an interlock with a bogus gas that is drier than breath. U.S. Pat. No. 3,824,537 teaches requiring the operator to place one hand on a button which must be activated during a test period while the other hand is used to hold a breath sampling tube located some distance away from the button. Since both hands of the operator are placed apart, deceptive manipulation of a bellows or the like is discouraged. While all of these techniques have some merit, they are of little overall benefit if a sobriety interlock can be circumvented regardless of them by the simple artifice of enlisting the aid of a sober accomplice to take the test. This vexing problem is dealt with in U.S. Pat. No. 4,738,333 to Collier et al.
The technique proposed in the above '333 patent is to require the operator/test subject to identify himself or herself by correctly performing what is termed an"identity-confirming act" which the interlock is capable of recognizing. Unless this act is correctly performed within a limited number of attempts, the interlock will not permit the vehicle to be started regardless of the result of any alcohol breath test. Unlike a personal identification number (PIN) code which can be readily entered by another person who is merely given knowledge of the code, correct performance of the identity-confirming act requires a degree of skill which cannot ordinarily be acquired by most persons without attempting the act at least some minimum number of times. The limited number of attempts the interlock allows the act to be tried is selected to be lower than the minimum number of attempts ordinarily required to learn the act. In this way, the interlock can effectively discriminate between a trained designated person and a previously unskilled accomplice.
Notwithstanding the advances of the prior art, reliable operation of a sobriety interlock cannot be ensured for extended periods without having the interlock serviced on a regular basis. This is particularly true where use of the interlock is compelled. Under such circumstances an interlock is more likely than usual to be subject to physical abuse or attempts to bypass the interlock by disconnecting it from the vehicle or otherwise. For this reason, routine operational checks of an interlock as well as physical inspection of both the interlock itself and the integrity of its connections to the vehicle should be conducted. Also, where the interlock includes information recording means, such as means for recording bypass events as disclosed herein, occasional attention to those recording means may be required for various purposes. For example, information may need to be read from such devices for the purpose of preparing periodic reports for review by a supervisory authority or to clear or replace the recording means to make room for new information and/or initiate a new recording period.
Even where use of an interlock is voluntary, being installed in a vehicle, it remains subject to extreme environmental conditions such as wide temperature and humidity variations, shock and vibration. The response characteristics of the alcohol sensing device used by the interlock are also subject to change due to the above factors, the effects of repeated usage, contamination from the environment or merely the passage of time. Any or all of these influences may make the operating characteristics of an interlock, particularly those related to alcohol measurement, subject to undesired variation necessitating some form of corrective action such as occasional calibration or perhaps even the replacement of the alcohol sensor or other components.
Should a significant change in the operating characteristics of a sobriety interlock occur for any reason, a variety of adverse consequences could result. Starting of the interlocked vehicle might not be enabled when it should be. Worse yet, the vehicle could be enabled to start when it should not be to the possible endangerment of the vehicle operator as well as the public. Perhaps even more seriously, normal running of the vehicle could be unexpectedly interrupted sometime after the vehicle is underway. Merely scheduling a service appointment is not considered to be an adequate safeguard against these possibly dire consequences. Appointments can be ignored, forgotten or, due to the exigencies of the moment, put off for a more convenient time.